Diolefin dimerization catalyst and method for producing nitrosyl halides of iron triad metals

ABSTRACT

A diolefin dimerization catalyst is disclosed which is formed by contacting components consisting essentially of at least one nitrosyl metal halide and at least one of elemental manganese, zinc, or tin. Also new methods for preparing nitrosyl halides of iron triad metals are disclosed.

This application is a division of application Ser. No. 964,326, filedNov. 29, 1978, now U.S. Pat. No. 4,181,707, which was a division ofapplication Ser. No. 817,471, filed July 20, 1977, now U.S. Pat. No.4,144,278.

This invention relates to the preparation of nitrosyl halides of an irontriad metal, i.e., iron, cobalt or nickel. In one aspect this inventionrelates to methods for preparing ligand-containing nitrosyl halidecomplexes of iron, cobalt, and nickel. In yet another aspect thisinvention relates to the dimerization of conjugated dienes with acatalyst employing an iron triad metal nitrosyl halide. In yet a furtheraspect, this invention relates to a novel composition of mattercomprising a diolefin dimerization catalyst employing an iron triadmetal nitrosyl halide.

While nitrosyl halides of iron, cobalt and nickel are known compounds,many prior art processes for synthesizing these materials are verytedious and time consuming and the yield of the desired compounds arequite low. An example is the process disclosed by Walter Hieber andReinhard Nast, "Chemical Abstracts", volume 35 (1941), column 2807-2808.In that process a compound of the formula Ni(NO)I was prepared by thesolid phase reaction of nickel iodide and zinc dust with nitric oxide.U.S. Pat. No. 3,481,710 disclosed an improved process for forming irontriad metal nitrosyl halides by reacting the metal dihalides with nitricoxide and the respective elemental iron triad metal or zinc. The presentinvention provides a new and simplified procedure for the production ofiron triad metal nitrosyl halides.

Therefore, one object of this invention is to provide a new, efficientmethod for the preparation of iron triad metal nitrosyl halides. Afurther object of this invention is to provide a method for theproduction of nitrosyl halides from readily available, easily handledmaterials. It is another object of this invention to provide a methodfor the production of ligand-containing nitrosyl halide complexes. It isyet another object of this invention to provide a method for thesynthesis of nitrosyl metal halides and complexed derivatives thereof ingood yields and of sufficient purity for use as catalyst components.Another object of this invention is to provide a new and improved methodfor dimerizing conjugated dienes. A still further object of thisinvention is to provide a new and improved catalyst system for thedimerization of conjugated dienes.

Other aspects, objects, and several advantages of this invention will beapparent to one skilled in the art from a reading of this disclosure andthe appended claims.

PRODUCTION OF NITROSYL HALIDES

In accordance with one embodiment of this invention, iron triad metalnitrosyl halides having the formula [Fe(NO)₂ X]_(y), [Co(NO)₂ X]_(y), or[Ni(NO)X]_(y), are prepared from the corresponding metal dihalidewherein X is either chlorine, bromine, or iodine, and y is 1 or 2 for Coand Fe and 1,2,3, or 4 for Ni by the reaction of the metal dihalide withan alkali metal nitrite in the presence of the corresponding elementaliron triad metal and/or elemental zinc in a liquid in which the metaldihalide is at least partially soluble and under reaction conditionssuitable for yielding said nitrosyl iron triad metal halide.

In accordance with another embodiment of the present invention, nitrosyliron halides and nitrosyl cobalt halides having the formulas as setforth above are prepared by a two-step process involving (1) reacting,in a liquid in which the corresponding iron triad metal dihalide is atleast partially soluble, the corresponding ferric halide or cobaltichalide with the corresponding elemental iron triad metal and/orelemental zinc under conditions suitable for producing a product mixturecontaining the corresponding iron triad metal dihalide and (2) reactingat least a portion of this iron triad metal dihalide with an alkalimetal nitrite under reaction conditions suitable for yielding saidcorresponding nitrosyl iron triad metal halide.

In accordance with another embodiment of this invention, nitrosyl nickelhalides, having the formula [Ni(NO)X]_(y), are prepared from thecorresponding nickel dihalide wherein X is either chlorine, bromine, oriodine, and y is 1,2,3 or 4, by the reaction of the nickel dihalide withan alkali metal nitrite in the presence of elemental nickel and/orelemental zinc in a liquid in which the nickel dihalide is at leastpartially soluble and under reaction conditions suitable for yieldingsaid nitrosyl nickel halide.

In accordance with yet another embodiment of the present invention,ligand-containing iron triad metal nitrosyl halides of the formulaFe(NO)₂ (L)X, Ni(NO)(L)X or Co(NO)₂ (L)X are prepared from thecorresponding metal dihalide wherein X is either chlorine, bromine oriodine by the reaction of the metal dihalide with an alkali metalnitrite in the presence of the corresponding elemental iron triad metaland/or elemental zinc and at least one compound (L) which forms ligandswith iron triad metal nitrosyl halides, said reaction being conductedunder conditions such that said ligand-containing iron triad metalnitrosyl halide is produced.

A still further embodiment of the present invention is the production ofligand-containing iron triad metal nitrosyl halides of the formulaFe(NO)₂ (L)X or Co(NO)₂ (L)X by the reaction of the corresponding metaldihalide wherein X is either chlorine, bromine, or iodine by thereaction of the metal dihalide with an alkali metal nitrite in thepresence of at least one compound (L) which forms ligands with irontriad metal nitrosyl halides, said reaction being conducted underconditions such that ligand-containing iron triad metal nitrosyl halideis produced.

In preparing the nitrosyl halides, any solvent for the iron triad metaldihalide can be employed which does not prevent the desired reaction.Specific examples of solvents suitable for use in preparing the nitrosylhalides in accordance with this invention include saturated mono- andpolyethers, which can be cyclic or acyclic and have from 3 to 20 carbonatoms per molecule and aromatic hydrocarbons having from 6 to 8 carbonatoms per molecule. The preferred solvents are those which have boilingpoints in the range of about 50° to about 100° C., or whose boilingpoints can be adjusted to that range by convenient manipulation of thereaction pressure. Any suitable amount of solvent can be employed,generally about 5 to about 50 parts of solvent is used per part of metaldihalide, by weight.

Some examples of suitable solvents are ethyl ether, methyl ether, butylether, methyl ethyl ether, tetrahydrofuran, p-dioxane,diglyme(diethylene glycol dimethyl ether), diethoxyethane,triglyme(triethylene glycol dimethyl ether), decyl cyclopropyl ether,2-ethylhexyl dodecyl ether, benzene, toluene, o-xylene, and the like andmixtures of any two or more thereof. Ethers are presently the preferredsolvents, tetrahydrofuran being particularly desirable.

The elemental iron triad metal and elemental zinc are preferablyemployed in a finely divided powder form. Generally, it is suitable toemploy elemental metal having average particle diameter in the range ofabout 0.037 mm to about 25 mm, preferably about 0.074 to about 0.25 mm.

Any suitable alkali metal nitrite can be reacted with the metaldihalides according to the embodiments described above. Examples ofsuitable alkali metal nitrites include lithium nitrite, sodium nitrite,potassium nitrite, rubidium nitrite, and cesium nitrite. Mixtures of anytwo or more of alkali metal nitrites may also be utilized if so desired.

In forming the ligand-containing iron triad metal nitrosyl halides, thecompound (L) can be any compound which forms ligands with iron triadmetal nitrosyl halides. Examples of suitable ligand-forming compoundsare those of the formulas

    R.sub.3 M, (RO).sub.3 M, SR', R--S--R, R.sub.3 MO, OR', and R--O--R

wherein each R is individually selected from the group consisting ofhydrocarbyl aromatic radicals, hydrocarbyl aliphatic radicals,halo-substituted hydrocarbyl aromatic radicals, halo-substitutedaliphatic hydrocarbyl radicals, alkoxy-substituted hydrocarbyl aromaticradicals and alkoxy-substituted aliphatic hydrocarbyl radicals, havingup to about 20 carbon atoms; wherein R' is a divalent saturated orolefinically unsaturated hydrocarbyl radical having 3 to 7 carbon atoms;and wherein M is phosphorus, antimony, or arsenic. When suchligand-forming materials are present in the reaction zone, the irontriad metal products have formulas Fe(NO)₂ (L)X, Ni(NO)(L)X, or Co(NO)₂(L)X where (L) represents the ligand-forming material used.

Some specific examples of suitable ligand-forming compounds aretributylphosphine, triphenylphosphine, triphenylphosphine oxide,trioctyl phosphite, tribenzylarsine, triphenyl stibonite, tricyclopentylarsonite, tris(4-bromophenyl)phosphite, trieicosylstibine,diphenylmethylphosphine, tris(2,4,6-trimethoxybenzyl)phosphine, methylsulfide, ethyl sulfide, methyl isobutyl sulfide, thiophene, and thelike, and mixtures of any two or more thereof. Where more than oneligand-forming compound is employed, the ligand-forming compounds whichresult in the most stable ligands will generally provide the predominantligand in the ligand-containing iron triad nitrosyl halide.

It should be noted that if the solvent employed in the present inventionis a ligand-forming compound, in order to recover the corresponding irontriad metal nitrosyl halide, the ligand will have to be removed bytechniques known in the art. For example, if ethers are utilized in thereaction of this invention as a suitable solvent, the product obtainedcan contain ether ligands. The ether ligand-containing iron triad metalnitrosyl halide can be readily converted to the nonligand-containingiron triad metal nitrosyl halide by the evaporation of the ether.

Any amounts of reactants can be employed which will result in theproduction of some of the desired product.

In the embodiments of the invention in which ferric halide or cobaltichalide are used as starting materials, the stoichiometry for thecomplete conversion of trihalide to dihalide requires that 1/2 mole ofelemental iron triad metal or elemental zinc be employed for every moleof trihalide to be reduced. Although less than such a stoichiometricamount can be used, such a procedure would result in poorer yields ofthe dihalide and accordingly poorer yields of the corresponding irontriad metal nitrosyl halide. It is therefore presently preferred thatthe amount of elemental iron triad metal and/or elemental zinc be atleast the stoichiometric amount. It is especially preferable if theamount of the elemental iron triad metal and/or elemental zinc employedis greater than the stoichiometric amount in order to providesubstantially complete conversion of the iron triad trihalide to thedihalide. Where excess elemental iron triad metal and/or elemental zincis employed in the reduction step, it is not necessary that separationof this excess from the products be made before the subsequent reactionwith the alkali metal nitrite to obtain the corresponding metal nitrosylhalide since that reaction can also be carried out in the presence ofelemental iron triad metal and/or elemental zinc. (It should be noted,however, that the presence of elemental iron triad metal and/orelemental zinc is not essential for the production of the correspondingmetal nitrosyl halide when iron dihalide or cobalt dihalide is reactedwith the alkali metal nitrite.)

While, as indicated in the preceding paragraph, zinc can be employed toaccomplish the reduction of the ferric or cobaltic halides, betteryields can be achieved by conducting such reduction with the respectiveelemental iron triad metal because at least a portion of the elementaliron triad metal can be converted into additional ferrous halide orcobaltous halide.

The amount of alkali metal nitrite reacted with the iron triad metaldihalide can be any amount which results in the production of iron triadmetal nitrosyl halide. Generally, the molar ratio of alkali metalnitrite to iron triad metal dihalide will be in the range of about 0.1/1to about 20/1. Higher or lower ratios could be employed but with obviouseconomic disadvantages. Preferably the ratio is in the range of about0.5/1 to about 6/1. It is especially preferred for the amount of alkalimetal nitrite to be since that at least about one-half of the iron triadmetal dihalide is converted to the corresponding nitrosyl metal halide.

As indicated above, when ferrous or cobaltous halide is reacted withalkali metal nitrite, elemental iron triad metal and/or elemental zincneed not be present for the production of the corresponding iron triadmetal nitrosyl halide. With nickel dihalide, however, in order to obtainnickel nitrosyl halide, elemental nickel and/or elemental zinc must bepresent when the nickel dihalide is reacted with the alkali metalnitrite. Any amount of the elemental nickel and/or zinc can be employedwhich will allow the production of the nickel nitrosyl halide.Generally, the molar ratio of the elemental metal to the nickel dihalideis in the range of about 0.1/1 to about 10/1, preferably 0.5/1 to about10/1.

The amount of ligand-forming compound, when employed, can be any amountwhich results in the production of ligand-containing iron triad metalnitrosyl halide. For economic reasons generally the molar ratio ofligand-forming compound to iron triad metal dihalide is in the range ofabout 0.1/1 to about 5/1, preferably about 0.5/1 to about 1.2/1. Toassure maximum yield, it is preferred that the molar ratio ofligand-forming compound to iron triad metal dihalide be at least about1/1.

The above reactions can be carried out at any temperature which do notprevent the productin of the nitrosyl metal product. For example, theconversion of ferric or cobaltic halides to dihalides can be carried outat any temperature sufficient to produce such dihalides. Generally, thiswould be a temperature in the range of about 25° to about 125° C., andpreferably about 50° to about 100° C. The reaction of the alkali metalnitrite and iron, cobalt or nickel metal dihalides (with or withoutligand-forming compound) can be carried out at any temperaturesufficient to produce the corresponding iron triad metal nitrosylhalide. Generally, this could be a temperature in the range of about 50°to about 200° C., preferably about 70° to about 150° C. It is oftenconvenient to carry out the reactions in refluxing diluent, thus thechoice of the diluent may determine the reaction temperature utilized.Any suitable pressure can also be employed in the above reactions.Generally, in the reaction of the alkali metal nitrite with the irontriad metal dihalide pressures in the range of about 25 to about 400psig are suitable. While the rate of the reaction was generally greaterat temperatures above 60° C., there was no observable pressure effect.

The reaction time for preparing the dihalides, the iron triad metalnitrosyl halides, and the ligand-containing iron triad metal nitrosylhalides is any length of time sufficient to provide a yield of thedesired product. The selection of suitable reaction time is well withinthe skill of those in this art. Generally, the ferric or cobaltichalides can be converted to the corresponding dihalides in less than onehour, although longer times can be employed if desired.

In the case of ferric halide reduction, the extent of reduction can beeasily determined by the change in color from orange color (ferric) to agray color (ferrous). Thus, when starting with ferric halide one canproceed to the second step of the reaction when the color of thereaction mixture has turned gray. It is not, however, necessary that allthe ferric or cobaltic halide be reduced to dihalide before the secondstep is initiated. Generally, the reaction of the alkali nitrite and theiron triad metal dihalide can be completed in less than one hour. Hereagain, however, longer times can be employed.

Since the nitrosyl metal halides produced according to this inventionare quite sensitive to water and oxygen, the amount of water and oxygenpresent should be below that which would prevent the formation of theiron triad metal nitrosyl halides or their ligand-containingcounterparts. It is therefore preferred that the reaction be carried outunder an inert atmosphere, for example nitrogen, argon, or helium, andthat the substances employed be at least substantially water-free. It isalso preferable to conduct the reactions with stirring which willachieve intimate contact of all the reaction ingredients.

The nitrosyl metal halides of iron, cobalt and nickel and theirligand-containing counterparts have utility as catalyst components forthe conversion of olefins or diolefins in reactions such asoligomerization, polymerization and the like. In particular, thenitrosyl iron halides prepared according to the instand invention haveutility in the dimerization of conjugated diolefins, i.e.,1,3-butadiene, isoprene and mixtures thereof, when combined with asuitable reducing agent according to the procedures taught in U.S. Pat.No. 3,377,397, Perry L. Maxfield. Also, the ligand-containing nitrosylnickel halides prepared in accordance with the present invention haveutility in the dimerization of monoolefins in accordance with theteachings of U.S. Pat. No. 3,427,365, Perry L. Maxfield.

DIMERIZATION REACTION AND DIMERIZATION CATALYST

In accordance with another embodiment of the instant invention, thecombination of (1) at least one nitrosyl metal halide selected from thegroup of nitrosyl halides having the formula [Fe(NO)₂ X]_(y), [Co(N0)₂X]_(y), [Ni(NO)S]_(y), Fe(NO)₂ (L)X, Ni(NO)(L)X, and Co(NO)₂ (L)X, asdefined above, with (2) at least one elemental metal selected frommanganese, tin, and zinc provides a novel catalyst system for thedimerization of conjugated diolefins. The use of elemental metals suchas manganese, zinc, or tin instead of the organometallic compounds usedin prior art dimerization processes offers several distinct advantages.For example, zinc, manganese, and tin metal is more easily handled thanthe pyrophoric and extremely air and water sensitive organometallicsused in prior art dimerizations. Furthermore, the metals manganese,zinc, and tin are much less expensive than the organometals which aredifficult to prepare and in many instances, difficult to store in auseable condition. Preferably the manganese, zinc and tin are employedin the form of finely divided metal powder. Generally, it is suitable toemploy the elemental metal in the form of particles having an averageparticle diameter in the range of about 0.37 mm to about 25 mm,preferably about 0.074 to about 0.25 mm.

The dimerization catalyst system mentioned in the previous paragraph issuitable for dimerizing a large number of conjugated diolefins.Typically the catalyst system can be utilized in the dimerization of oneor more acyclic conjugated dienes having from 4 to 12 carbon atoms permolecule. Examples of such suitable conjugated dienes are isoprene,1,3-butadiene, piperylene, 2,3-dimethyl-1,3-butadiene, 1,3-hexadiene,2,4-octadiene, 2-methyl-1,3-pentadiene, 4-ethyl-1,3-decadiene, and thelike, and mixtures of any two or more thereof.

It should be noted that generally the crude product mixture resultingfrom the preparation of the nitrosyl halide derivative cocatalyst inaccordance with this invention can be employed directly in thedimerization process. That is, it is not generally necessary to use thenitrosyl halide derivative cocatalyst in its isolated form. Occasionallythough, if the product mixture contains certain of the ligand-formingcompounds in too great an extent, the ligand-forming compounds may exertan inhibiting effect upon the dimerization. Such has been noted for acrude reaction mixture containing excess triphenyl phosphine.

Preferably, a diluent or solvent, substantially nonreactive with theother components, is employed in the dimerization reaction. Particularlypreferred diluents include saturated mono- and polyethers, which arecyclic or acyclic and have from 3 to 20 carbon atoms per molecule andaromatic hydrocarbons having 6 to 8 carbon atoms per molecule. Examplesof suitable diluents include pentane, heptane, cyclohexane, benzene,toluene, xylene, chlorobenzene, methylene chloride, tetrahydrofuran, andthe like, and mixtures of any thereof.

The above-described first and second catalyst components can be combinedin any amounts which result in an active catalyst, generally they arecombined, for use in this invention, in proportions such that the moleratio of the aforementioned elemental metal to the nitrosyl metal halideis in the range of about 0.75/1 to about 50/1, and preferably in therange of about 1/1 to about 30/1. Any catalytic amount of the nitrosylmetal halide containing catalyst can be employed. The mole ratio ofdiolefin to the nitrosyl metal halide for practical purposes isgenerally in the range of about 50/1 to about 50,000/1, preferably about500/1 to about 5,000/1.

The order in which the catalyst components and the diolefin feed arecombined is not considered to be critical. Of course, since the nitrosylmetal halides are sensitive to both oxygen and water, suitable stepsshould be taken to minimize the effects of those materials. Preferablythe catalyst components and the diolefin feed are combined under aninert atmosphere and the inert atmosphere is maintained during thedimerization. A suitably inert atmosphere can be provided by gases suchas nitrogen, argon, etc. Also it is preferred that the diolefinic feedbe free of any deleterious amounts of materials which act as catalystpoisons, such as oxygen, water, allenes, and acetylenes.

According to this invention, the dimerization occurs when the diolefinis contacted with the catalyst at a temperature which allows productionof the dimer. Generally, suitable temperatures are in the range of about0° to about 100° C., and preferably are in the range of about 20° toabout 80° C. The dimerization can be carried out at any convenientpressure which is sufficient to maintain the reaction mixture in asubstantially liquid state. Generally, pressures ranging from 0 to about1,000 psig can be used. The contact time will vary according to theefficiency of the contacting technique, the reaction temperature, andthe desired degree of conversion, but will generally be in the range offrom about 1 minute to about 10 hours, preferably in the range of about30 minutes to about 5 hours. Generally, the reaction time is quite lowsince the cataysts of this invention are very active even at lowtemperatures. The dimerization can be carried out in a batch process orcontinuous process or even in a semi-continuous process whereinbutadiene is intermittently charged as needed to replace that alreadydimerized. Generally, in a continuous dimerization process, the grams ofconjugated diene per gram of iron triad catalyst per hour is in therange of about 3/1 to about 30,000/1, preferably about 1,000/1 to about2,000/1. Any suitable reactor system can be employed. A very usefultechnique involves passing a solution of the iron triad metal nitrosylhalide along with the diolefin through a bed of particulate elementalSn, Mn, or Zn metal.

At the end of the dimerization, the dimer can be recovered by anysuitable conventional methods such as fractional distillation, solventextraction, adsorption techniques, etc.

The dimerization process of this invention has particular utility inobtaining purer diolefin from a hydrocarbon fraction containing otherhydrocarbons which boil at approximately the same temperature as thediolefin. For example, the dimerization is useful in the treatment of C₄refinery streams which contain conjugated dienes such as 1,3-butadieneand other hydrocarbons boiling within about 30° F. of the boiling pointof the 1,3-butadiene. The treatment typically would involve treating theC₄ fraction to eliminate deleterious amounts of acetylenes, 1,2-dienes,oxygen and water. Then the C₄ fraction would be subjected todimerization in accordance with this invention. The dimerization productwould then be separated into a first heavy fraction of vinylcyclohexeneand materials of higher boiling point than vinylcyclohexane and a firstlight fraction of hydrocarbons of lower boiling point thanvinylcyclohexene.

The first heavy fraction can then be separated by a technique such assteam stripping into a second heavy fraction of materials of higherboiling point than vinylcyclohexene and a second light fraction ofvinylcyclohexene. The second light fraction, viz, vinylcyclohexene wouldbe passed along with steam into a cracking zone wherein vinylcyclohexenewould be converted into 1,3-butadiene. The effluent from the crackingzone could be cooled to recover a water phase which can be removed,converted into steam and reused in the cracking operation. After thecondensed water is removed, the effluent from the cracking zone can beseparated into a third heavy fraction containing vinylcyclohexene andmaterials having boiling points greater than vinylcyclohexene and athird light fraction containing materials having lower boiling pointsthan vinylcyclohexene. The third heavy fraction can be recycled to thecracking zone. The third light fraction can be separated into a fourthlight fraction containing 1,3-butadiene and materials having lowerboiling points than 1,3-butadiene and a fourth heavy fraction ofmaterials having boiling points greater than 1,3-butadiene. The fourthlight fraction could then be separated into a fifth light fractionconsisting of materials having boiling points lower than that of1,3-butadiene and a fifth heavy fraction containing 1,3-butadiene in amore concentrated form than the original C₄ feed which is subjected todimerization. Generally, in such a process the fifth light fraction andthe fourth heavy fraction could be directed so that they could be addedto the dimerization zone along with C₄ feed.

Of course the dimers obtained from the dimerization process of thisinvention can be isolated and used for other purposes which are wellknown in the art. For example, 4-vinylcyclohexene obtained from1,3-butadiene can be converted to styrene or1,2-bis(3-cyclohexene-1-yl)ethylene.

The preparation of iron triad metal nitrosyl halides and the use ofthose materials for dimerization both in accordance with this inventionwill be further illustrated by the following examples. In the followingexamples, the elemental metals employed had an average particle diameterin the range of about 0.074 mm to about 0.149.

EXAMPLE I

The runs of this example for the preparation of the iron nitrosyl halideaccording to the process of the invention utilized triphenyl phosphineas the ligand-forming compound in the iron nitrosyl halide preparationstep. For convenience, the iron nitrosyl halide preparations in theexamples will be identified by a catalyst number though it will berecognized that in the dimerization runs the additional metal catalystcomponent is also present in the dimerization catalyst.

Catalyst No. 1 was prepared by charging 3.1 grams (19.1 mmol) of ferricchloride, 1.2 grams (21.5 mg-atom) of iron powder, 6 grams (87 mmol) ofsodium nitrite and 5 grams (19.1 mmol) of triphenyl phosphine to a 250ml Schlenk flask. The flask was evacuated and 100 ml of tetrahydrofuran(THF) was added to the flask. The flask was heated at reflux for 3hours, then cooled and filtered to obtain a dark brown/black filtrate.Said filtrate was allowed to stand overnight. The THF was removed fromthe filtrate under vacuum at room temperature to leave a black tarrymaterial which was insoluble in pentane. After additional evacuationtreatment, 100 ml of THF was added to the filtrate to provide a solutionthat was approximately 0.2 molar in iron. Said solution was stored undernitrogen at a low temperature.

Catalyst No. 2 was prepared by charging 1 gram (6.2 mmol) of ferricchloride, 0.68 grams (12.2 mg-atom) of iron powder, 1.60 grams (6.1mmol) of triphenyl phosphine and 0.84 grams (12.2 mmol) of sodiumnitrite to a 250 ml Schlenk flask. THF (40 ml) was added to the mixtureand the resulting mixture heated for 2 hours at reflux. The mixture wasallowed to stand overnight and then refluxed for an additional 1 hour.The reaction mixture was cooled and filtered to obtain a brown-blackfiltrate.

Catalyst No. 3 was prepared employing an excessive amount of triphenylphosphine by charging 1 gram (6.2 mmol) of ferric chloride, 0.68 grams(12.2 mg-atom) of iron powder, 3.40 grams (13 mmol) of triphenylphosphine and 0.7 grams (10.1 mmol) of sodium nitrite to a 100 mlSchlenk flask under a nitrogen atmosphere. THF (40 ml) was added to themixture and the mixture heated at reflux with stirring for three hours.At the end of this time, it was cooled to room temperature and left tostand under nitrogen. The mixture was later filtered and the filtrateutilized as the catalyst component in a 1,3-butadiene dimerization runas described below.

Each of the nitrosyl iron chloride preparations described above wereutilized in 1,3-butadiene dimerization reactions. The dimerizationreactions were carried out in a Fisher-Porter aerosol compatibilitybottle as the reaction vessel. In some of the runs, additional THF wasadded to the reactor as a diluent while in other runs no additionaldiluent was utilized in the dimerization reaction. Each of the reactionmixtures was analyzed by gas-liquid phase chromatography (GLC). Theamounts of reactants and reaction conditions utilized in the butadienedimerization runs as well as the results obtained in said runs arepresented in Table I below. It will be noted that tin metal was utilizedas the reducing agent for the nitrosyl iron chloride catalyst componentin the dimerization runs.

                                      TABLE I                                     __________________________________________________________________________               Charge                                                             Run                                                                              Time,                                                                             Temp.,                                                                            Catalyst (Fe)                                                                         Sn,    THF,                                                                              Bd, 4-VCH %                                     No.                                                                              hr. °C.                                                                        No.                                                                              mmol (a)                                                                           g(mg-atom)                                                                           ml  g   Yield (b)                                   __________________________________________________________________________    1  1.5 60  1  1.2  1.3 (11)                                                                             0   ca. 18                                                                            ca. 80(c)                                   2  5   50  1  1.0  0.7 (5.9)                                                                            0   22.5                                                                              95                                          3  5   60  2  0.69 0.6 (5)                                                                              8   17.1                                                                              >90                                         4  5   60  2  0.69 0.5 (4.2)                                                                            10  15.2                                                                              76                                          5  4   60  2  0.69 0.7 (5.9)                                                                            10  16.4                                                                              89                                          6  5   60  2  0.69 0      10  5.5 0                                           7  ca. 12                                                                            60  3  0.69 0.7 (5.9)                                                                            10  14.4                                                                              0                                           __________________________________________________________________________     Estimated value based on expected concentration of ferrous chloride from      reaction of FeCl.sub.3 with Fe(O) and optimum reaction of FeCl.sub.2 with     NaNO.sub.2.                                                                   (b) Yield based on 1,3butadiene charged to reaction mixture.                  (c) Quantitative analysis not made.                                      

The above results demonstrate that catalysts prepared according to theinstant invention are active for the dimerization of 1,3-butadiene to4-vinylcyclohexene in good yield. Run No. 6 demonstrates that without areducing agent (Sn metal) the iron catalyst component is inactive fordimerization. The lack of dimerization in Run No. 7 is believed to bedue to presence of excess triphenyl phosphine in the nitrosyl catalystcharge.

EXAMPLE II

Other runs were carried out according to the instant invention in whichthe iron nitrosyl chloride component was prepared in the presence oftriphenylphosphine oxide as the ligand-forming compound.

Catalyst No. 4 was prepared by charging 1 gram (6.2 mmol) of ferricchloride, 0.68 grams (12.2 mg-atom) of iron powder, 1.70 grams (6.1mmol) of triphenylphosphine oxide and 0.7 grams (10.1 mmol) of sodiumnitrite to a 100 ml Schlenk flask under a nitrogen atmosphere. THF (40ml) was added to this mixture and the mixture heated at reflux withstirring for 3 hours. At the end of the 3 hour reaction period, thereaction was terminated and allowed to stand at room temperatureovernight. An aliquot of the mixture was removed for isolation andexamination of the solid and one-half of the remainder was placed in atube under nitrogen for later use as catalyst. The aliquot portion wastreated to remove the THF by vacuum and then benzene and heptane wereadded to give a semi-solid material. Evaporation of these liquids left adark brown solid. This material was examined by infrared analysis whichindicated the presence of two nitrosyl ligands whose absorption best fitthose expected for the compound Fe(NO)₂ (triphenylphosphine oxide)Cl.

Catalyst No. 5 was prepared in the same manner as that described forcatalyst No. 4. After the reaction mixture had refluxed for 3 hours, themixture was cooled and filtered and the filtrate retained for use indiene dimerization reactions.

Next a preparation was conducted on a larger scale than the two previousruns of the instant example. In this preparative run, there was added 10grams (61.6 mmol) of ferric chloride, 7 grams (125.3 mg-atom) of ironpowder, 17 grams (61.1 mmol) of triphenylphosphine oxide, and 7 grams(101.4 mmol) of sodium nitrite to a 500 ml Schlenk flask under anitrogen atmosphere. THF (250 ml) was added to the mixture and stirredfor 3 hours at room temperature. The mixture was then heated at refluxfor 3 hours during which it became dark brown in color. The mixture wascooled for about 0.5 hours and then filtered through a medium porosityfritted glass filter and 220 ml of the solution was transferred to asealed vessel under a nitrogen atmosphere. The remainder of the solutionshowed some olive colored solid precipitating out so it was cooled in arefrigerator for 3 days to facilitate the precipitation of the solid.Following this, the solvent was removed from the solution and the tarryremains were evacuated at about 25° C. under a pressure of 10⁻⁴atmospheres for 1.5 days. To this material 70 ml of THF were added andthe resulting solution, which was brown/green in color, was stirredvigorously for 0.5 hours. The mixture was then treated with 40 ml ofn-heptane added slowly under nitrogen while being stirred. A solidprecipitate was recovered by filtration from the solution using a mediumporosity fritted glass filter. The solid was washed with 20 and 10 mlportions of n-pentane and dried under vacuum. Both the isolated solidmaterial and the initial filtrate from the reaction mixture contain theactive nitrosyl iron chloride catalyst component. The solid is heredenoted Catalyst No. 6A and the filtrate Catalyst No. 6B.

Catalyst No. 7 was prepared utilizing the same amounts of reactants asin the preparation of catalyst No. 6 but with a slightly differentreaction procedure. In this instance, the mixture with 200 ml THF wasstirred for 0.5 hour at room temperataure and then for 3 hours atreflux. The mixture was filtered through a coarse porosity fritted glassfilter while still hot. The solid material was precipitated from the THFsolution by the addition of n-heptane. The precipitated solid was stilltacky even after washing with n-pentane. Some inadvertent contact withair may have occurred with the solid while it was left overnight.

Catalyst No. 8 was prepared by charging 20 grams (123.3 mmol) of ferricchloride, 14 grams (250.7 mg-atom) of iron powder, 34 grams (122.2 mmol)of triphenylphosphine oxide, and 14 grams (202.9 mmol) of sodium nitriteto a 500 ml Schlenk flask under a nitrogen atmosphere. THF (250 ml) wasadded to this mixture under nitrogen and refluxed for 4 hours. Themixture was cooled and filtered. The filtrate was taken to dryness undervacuum and the remaining solid material was extracted with hot THF butonly a small amount of material was apparently removed in thisextraction step. THF (100 ml) was added to the residue remaining fromthe evaporated filtrate and there was produced a dark brown solution towhich was added 100 ml of n-heptane with additional stirring. Thismixture was then evaporated with cooling to precipitate a solid materialand then filtered. The solid was then washed with n-pentane until thepentane washings were colorless. The solid material obtained in thisfiltration step was dried under vacuum to give 34.5 grams of dark brownsolid. The extracted residue from the original reaction mixture was alsorecovered and it weighed 38 grams. Presumably this residue materialcontained very little THF as a compound or in combination with thenitrosyl halide as a ligand.

The catalyst materials prepared as described were utilized in a numberof dimerization runs for 1,3-butadiene. These runs utilized a variety ofmetals as reducing agents for the nitrosyl iron chloride catalystcomponent and in some instances, without additional THF being added tothe reaction mixture. The results of said dimerization runs arepresented below in Table II along with the reaction conditions employedand the amounts of the catalyst utilized.

                                      TABLE II                                    __________________________________________________________________________    Run                                                                              Time, Temp., Catalyst (Fe)                                                                        Metal,                                                                             THF,                                                                              Bd,                                                                              4-VOH                                      No.                                                                              hr.   °C.                                                                           No.                                                                              mmol                                                                              (mg-atom)                                                                          ml  g  % Yield(d)                                 __________________________________________________________________________    1  ca. 16                                                                              60     4  0.69(a)                                                                           Sn(5)                                                                              10  19  95                                        2  ca. 16                                                                              60     5  0.46(a)                                                                           Sn(6.7)                                                                            10  23 ca. 100                                    3  5     60     6A 0.35(b)                                                                           Sn(4.6)                                                                            5   9.6                                                                              (c)                                        4  3.5   60     6B 1.85(a)                                                                           Zn(7.6)                                                                            5   17.2                                                                             ca. 80                                     5  0.5   110                                                                                  6B 1.85(a)                                                                           Mn(18.2)                                                                           5   25.1                                                                             >50                                           2     80                                                                   6  1.5   65-70  7  0.7(b)                                                                            Sn(2.5)                                                                            5   19.6                                                                             ca. 100                                    7  18    65     8  0.7(b)                                                                            Zn(0.8)                                                                            0   9.1                                                                              ca. 95                                     8  2.5   65-70  8  0.7(b)                                                                            Sn(2.5)                                                                            5   16.8                                                                             ca. 100                                    __________________________________________________________________________     (a)Estimated value based on expected concentration of ferrous chloride        from reaction of FeCl.sub.3 with Fe(O).                                       (b)Charged solid material believed to be: Fe(NO).sub.2 ((phenyl).sub.3        PO)Cl.                                                                        (c) A large amount of 4VCH was observed in the GLC analysis but no            estimate of yield was made.                                                   (d)Yield based on 1,3butadiene charged to reaction mixture.              

EXAMPLE III

In a control run, the following reaction mixture was prepared in aFisher-Porter aerosol compatibility bottle: 0.25 grams (1.5 mmol) offerric chloride, 0.3 grams (2.5 mg-atom) of tin powder and 0.3 grams(4.5 mmol) of sodium nitrite. The bottle reactor was evacuated thenflushed with nitrogen followed by the addition of 10 ml of THF. Themixture was cooled with dry ice and 18.3 grams (339 mmol) of1,3-butadiene added. This reaction mixture was heated to 75° C. withstirring. During this time, the original dark green solution changed incolor to an orange-brown color. After 5 hours, the reaction wasterminated and the reaction mixture allowed to cool to room temperatureand stand for 1 day. Pressure on the reactor was still at 25 psigindicating there had been little, if any, conversion of 1,3-butadiene tothe dimer. The results of this run indicate that one does not obtaindimerization of 1,3-butadiene to 4-vinylcyclohexene if one attempts toform the iron nitrosyl halide simultaneously with the dimerization.

EXAMPLE IV

Catalyst No. 6B of Example II above was utilized in a series of runs forthe dimerization of butadiene with elemental tin as a reducing agent inthe presence of added olefinic compounds such as isobutylene andcis-2-butene.

In run No. 1 of this example, a Fisher-Porter aerosol compatibilitybottle was charged with 2 ml (ca. 0.74 mmol) of the nitrosyl ironchloride catalyst component No. 6B, 5 ml of THF, 0.9 grams (7.6 mg-atom)of tin powder, 9.5 grams (176 mmol) of 1,3-butadiene and 8.1 grams (145mmol) of isobutylene. The above reaction mixture was heated at 60° C.for 5 hours and then allowed to cool and stand overnight. Later, 1 ml ofn-undecane was added to the reaction vessel to use as an internalstandard for gas-liquid phase chromatography (GLC) analysis. Althoughreliable quantitative analysis results were not obtained in this run, itwas apparent that the catalyst system was active for the dimerization of1,3-butadiene in the presence of large amounts of isobutylene.

Run No. 2 of the instant example was carried out by charging aFisher-Porter aerosol compatibility bottle with 2 ml (ca. 0.74 mmol) ofthe nitrosyl iron chloride catalyst component No. 6B, 5 ml of THF, 0.6grams (5 mg-atom) of tin powder, 13.5 grams (250 mmol) of 1,3-butadieneand 9.9 grams (177 mmol) of cis-2 -butene. The reaction mixture wastreated in the same manner as that described for run No. 1 of thisexample. In this run GLC analysis indicated a 70% yield of the4-vinylcyclohexene dimer based on the amount of 1,3-butadiene charged.This result also indicated that the catalyst system described was activefor the dimerization of 1,3-butadiene to 4-vinylcyclohexene in thepresence of large amounts of cis-2-butene.

Run No. 3 was carried out by charging a Fisher-Porter aerosolcompatibility bottle with 2 ml (ca. 0.74 mmol) of the nitrosyl ironchloride catalyst component No. 6B, 5 ml of THF, 0.6 grams (5 mg-atom)of tin powder, and 12.4 grams (230 mmol) of 1,3-butadiene. This mixturewas treated in essentially the same manner as the previous two runs ofthis series. Gas-liquid phase chromatography analysis showed a 96% yieldof 4-vinylcyclohexene from 1,3-butadiene in this run. The apparent highyield of the dimer in the latter run compared to the previous two runsindicate that dimer yield may be somewhat lower when the dimerizationreaction is carried out in the presence of olefinic compounds such asisobutylene or cis-2-butene.

EXAMPLE V

Another dimerization run with the iron nitrosyl chloride catalystcomponent No. 6B of Example II was carried out. In this dimerizationrun, the 1,3-butadiene was present in admixture with several other C₄hydrocarbons to simulate a refinery C₄ stream. The composition of thesynthetic C₄ stream was as follows:

    ______________________________________                                        Stream Component      Weight, %                                               ______________________________________                                        Isobutane             2.26                                                    Isobutene             27.73                                                   Cis-2-butene          5.03                                                    n-Butane              5.02                                                    Trans-2-butene        7.17                                                    1-Butene              16.49                                                   1,3-Butadiene         36.30                                                   ______________________________________                                    

In the instant run, a Fisher-Porter aerosol compatibility bottle wascharged with 5 ml (ca. 1.85 mmol) of catalyst component No. 6B, 5 ml ofTHF, 0.7 grams (5.9 mg-atom) of tin metal powder and 19.6 grams (132mmol 1,3-butadiene) of the above-described C₄ hydrocarbon mixture. Theabove-described reaction mixture was heated to 65° C. with stirring for24 hours. After standing at room temperature for 1 week, 2 ml ofn-undecane was added to the mixture as an internal standard for GLCanalysis. Two analyses showed the presence of 4-vinylcyclohexene in88.72% yield in one analysis and 92.69% yield in the second analysis.The yield figures are based upon the amount of 1,3-butadiene in theoriginal reaction mixture. These results indicate that the catalyst wasquite active toward dimerization of 1,3-butadiene in the presence ofother C₄ hydrocarbons, such as might be found in a typical refinery C₄stream.

EXAMPLE VI

Catalyst No. 9 was prepared to demonstrate the preparation of an activecatalyst without the addition of a ligand-forming compound other thanthe ether (tetrahydrofuran) utilized in the preparation step. In thisrun, there was added 5 grams (30.8 mmol) of ferric chloride and 1 gram(17.9 mg-atom) of iron powder to a 500 ml Schlenk flask followed by theaddition of 100 ml of THF under a nitrogen atmosphere. This mixture wasstirred under reflux conditions until the solution turned from itsoriginal red-brown color to gray, which indicated the production of theferrous halide. Then, there was added to the reaction vessel 2.2 grams(31.9 mmol) of sodium nitrite and the mixture stirred under reflux fortwo hours. The mixture was allowed to stand at room temperatureovernight with stirring.

Dimerization of 1,3-butadiene present in a synthetic C₄ stream havingthe same composition as that employed in Example V was conducted bycharging 10 ml (ca. 4.62 mmol) of catalyst No. 9, 0.35 grams (5.4mg-atom) of zinc powder and 31.2 grams of a C₄ stream which contained11.326 grams (210 mmol) of 1,3-butadiene. The temperature of the mixturewas increased from 15° C. to 55° C. over a 4-hour period and allowed tocool at room temperature. There was added to the mixture 1.6 grams ofdodecane as an internal standard for gas-liquid phase chromatography(GLC) analysis. Said analysis indicated the presence of 9.24 grams of4-vinylcyclohexene for a yield of 81.6% based on the 1,3-butadienepresent in the original reaction mixture.

A second run was carried out by utilizing 5 ml (ca. 2.31 mmol) of thecatalyst No. 9, 0.35 grams (5.4 mg-atom) of zinc powder, 0.2 grams ofpotassium iodide and 22.7 grams (420 mmol) of 1,3-butadiene. Thereaction was carried out over a period of about 21/2 hours with thetemperature being increased 21°-50° C. At the conclusion of thereaction, the mixture was allowed to cool and 1.65 grams of dodecane wasadded to the mixture as an internal standard for GLC analysis. Saidanalysis indicated the presence of 19.628 grams of 4-vinylcyclohexenefor a yield of 86.5% based on the 1,3-butadiene charged to the reactionmixture. It is not believed that the presence of the potassium iodidehad any significant effect on the yield of the 4-vinylcyclohexeneproduced in the instant run.

EXAMPLE VII

A run was carried out charging an amount of tin powder sufficient forthe dimerization reaction to a mixture comprising the ferric chloride,triphenylphosphine oxide, and sodium nitrite in THF. The run was carriedout by charging 5 grams (30.8 mmol) of ferric chloride, 7 grams (59mg-atom) of tin powder, 8.5 grams (30.5 mmol) of triphenylphosphineoxide and 3.5 grams (50.7 mmol) of sodium nitrite and 100 ml of THF to a200 ml Schlenk flask. The mixture was refluxed for 3 hours during whichtime the mixture changed color from a dark green to a dark red-brownwhich is characteristic of the nitrosyl iron chloride complex withtriphenylphosphine oxide as a ligand.

The above mixture was tested for its dimerization activity by charging 5ml of the reaction mixture with 5 ml of additional THF and 8.5 grams(157 mmol) of 1,3-butadiene to a Fisher-Porter aerosol compatibilitybottle. This mixture was heated to 60° C. with stirring overnight.Analysis of the mixture by gas-liquid phase chromatography showed thepresence of a substantial amount of 4-vinylcyclohexene. No attempt wasmade to determine the quantitative yield of the cyclic dimer. Thisresult, however, does demonstrate that a one-step preparation of thedimerization catalyst is possible.

A portion of the one-step catalyst preparation described above was takento dryness and 0.6 grams of this solid material was utilized for thedimerization of 1,3-butadiene (12.7 grams, 235 mmol) in 10 ml of THF.The mixture of catalyst, solvent, and 1,3-butadiene was stirred in aFisher-Porter aerosol compatibility bottle at 60° C. for 5 hours.Essentially no change in the pressure on the vessel was noted duringthis reaction time. The mixture was allowed to stand overnight at roomtemperature (ca. 23° C.) and 0.74 grams of n-undecane added to themixture as an internal standard for GLC analysis. Said analysisindicated only a small amount of 4-vinylcyclohexene was present. Closeexamination of the remaining solid from the one-step catalystpreparation indicated that it had been oxidized, probably by accidentalcontact with air. This is expected to have been the reason for the lowyield of 4-vinylcyclohexene in the dimerization reaction.

EXAMPLE VIII

Catalyst No. 10 was prepared according to the instant invention whereinferrous chloride (FeCl₂) was reacted directly with sodium nitrite in thepresence of tetrahydrofuran (THF) to produce the iron nitrosyl chloridecatalyst component. In this run, a 100 ml Schlenk flask was charged with1 gram (7.9 mmol) of ferrous chloride which had been previously dried byheating under reduced pressure, 2 grams (29 mmol) of sodium nitrite and30 ml of THF. The resulting dark green solution was stirred undernitrogen at reflux temperature of the THF and after about 0.5 hours, thesolution had become dark brown. Refluxing of the reaction mixture wascontinued for a total of 1.5 hours.

A Fisher-Porter aerosol compatibility bottle was charged with 1 ml ofcatalyst No. 10 reaction mixture (equivalent to 0.26 mmol of ferrousiron), 0.3 grams (4.6 milligram atoms) of zinc powder, 10 ml THF and14.2 grams (263 mmol) of 1,3-butadiene. The dimerization reactionmixture was stirred while heating to a temperature of about 70° C. inabout 1 hour and stirring was continued while the temperature was thenallowed to cool to room temperature over a period of about 1 hour afterwhich there was added 1.58 grams of n-dodecane as an internal standardfor gas-liquid phase chromatography analysis. The GLC analysis indicateda 106% yield of 4-vinylcyclohexene had been obtained in the dimerizationrun. This yield figure indicated a possible weighing error had been madebut in any event demonstrated that catalyst No. 10, which had beenprepared directly by the reaction of ferrous chloride with sodiumnitrite in THF, was a very active catalyst component for thedimerization of 1,3-butadiene to 4-vinylcyclohexene.

EXAMPLE IX

Catalyst No. 11 was prepared according to the instant invention whereina 500 ml Schlenk flask was charged with 8 grams (49 mmol) of anhydrousferric chloride, 6 grams (107 mmol) of iron powder and 11 grams (159mmol) of sodium nitrite. The flask was also charged with 250 ml ofdistilled 4-vinylcyclohexene as the reaction diluent and a stirringmeans (magnetic stirring bar). The reaction utilizing the abovecomponents was carried out by adding the ferric chloride and iron powderto the 4-vinylcyclohexene first and refluxing this mixture for 1 hourfollowed by the addition of sodium nitrite. The resulting mixture wasrefluxed for two additional hours. It was observed that the mixture atthis time was essentially the same color as that observed for thepreparation of the iron nitrosyl chloride catalyst in tetrahydrofuransolvent. At the end of the 3-hour reaction period, the solution wascooled and filtered. A large amount of unreacted or insoluble solidmaterial was recovered. Presumably, this relatively large amount ofrecovered solid material was due to the poorer solvating ability of the4-vinylcyclohexene in comparison to previously utilized tetrahydrofuran.

The activity of the above-described catalyst No. 11 in the dimerizationof 1,3-butadiene was examined by charging 2 ml of said filtered solution(about 1.8 mmol Fe) with 0.7 grams of zinc powder and 20 grams of1,3-butadiene to a Fisher-Porter aerosol compatibility bottle. Thisdimerization reaction mixture was maintained at 65°-70° C. for 2 hoursafter which analysis by gas-liquid phase chromatography of saiddimerization reaction mixture showed a greater than 85% conversion ofthe 1,3-butadiene to 4-vinylcyclohexene. The exact amount of conversioncould not be readily determined in the analysis because of the added4-vinylcyclohexene in the catalyst component solution.

The results of the above-described dimerization of 1,3-butadieneindicate that the iron nitrosyl chloride prepared as described above inthe absence of any liquid or ligand-forming compound was active as a1,3-butadiene dimerization catalyst component.

EXAMPLE X

Another catalyst (No. 12) was prepared by reacting ferric chloride, ironpowder and sodium nitrite in the presence of triphenylphosphine oxidefor the production of an iron nitrosyl chloride. See previous runs ofExample II for catalyst preparations utilizing triphenylphosphine oxideas the ligand-forming compound. The catalyst was prepared by chargingFeCl₃, 4 g (24.6 mmol) and 100 ml tetrahydrofuran (THF) to a 200 mlSchlenk flask equipped with stirring means. To the stirred mixture ofFeCl₃ and THF was added Fe powder, 2.8 g (50.1 mg-atoms), NaNO₂, 2.8 g(40.6 mmol), and triphenylphosphine oxide, 6.8 g (24.4 mmol). Theresulting mixture was stirred at about 25° C. for 15 minutes then heatedat reflux temperature (about 65° C.) for 3 hours under a nitrogenatmosphere. The mixture was cooled and transferred to a dried beveragebottle under nitrogen. The bottle was capped, flushed with nitrogenthrough the cap having a self-sealing rubber liner, and stored undernitrogen.

Catalyst No. 12 was utilized in a dimerization run employing isoprene asthe conjugated diene reactant. In this run a Fisher-Porter aerosolcompatibility bottle (177 ml) was charged with 0.7 g (5.9 mg-atoms) oftin powder, 5 ml (about 2.5 mmol Fe) of catalyst No. 12 preparation and20 ml (13.62 g) of isoprene. The dimerization run was allowed to reactat 65° C. overnight (about 16 hours). At the end of the run, the reactorwas cooled and vented. The liquid products were analyzed by gas-liquidphase chromatography after 2 ml of n-undecane had been added as aninternal standard for the analysis. The analysis showed 82% conversionof isoprene with an 88% selectivity to one dimer (apparently limonene)and an overall 98% selectivity to all dimeric species.

The results of the isoprene dimerization run carried out with thecatalyst according to the instant invention demonstrate that isoprene isvery readily converted to the dimeric species according to the instantinvention.

Although this invention has been described in considerable detail, itmust be understood that such detail is for the purpose of illustrationand that many variations and modifications can be made by one skilled inthe art without departing from the spirit and scope of the inventionherein disclosed and claimed.

What is claimed is:
 1. A catalyst system formed by contacting componentsconsisting essentially of (1) at least one elemental metal selected fromthe group consisting of manganese, tin, and zinc with (2) at least onenitrosyl metal halide selected from the group consisting of nitrosylmetal halides having the formulas [Fe(NO)₂ X]_(y), [Co(NO)₂ X]_(y),[Ni(NO)X]_(y), Fe(NO)₂ (L)X, Ni(NO)(L)X, and Co(NO)₂ (L)X, wherein X isselected from the group consisting of chloride, bromide, and iodide, yis 1 or 2 for Co and Fe and 1, 2, 3, or 4 for Ni, and wherein (L) isselected from the group of compounds having the formulas

    R.sub.3 M, (RO).sub.3 M, SR', R--S--R, R.sub.3 MO, OR', and R--O--R

wherein each R is individually selected from the group consisting ofhydrocarbyl aromatic radicals, hydrocarbyl aliphatic radicals,halo-substituted hydrocarbyl aromatic radicals, halo-substitutedaliphatic hydrocarbyl radicals, alkoxy-substituted hydrocarbyl aromaticradicals and alkoxy-substituted aliphatic hydrocarbyl radicals having upto about 20 carbon atoms, wherein R' is a divalent saturated orolefinically unsaturated hydrocarbyl radical having 3 to 7 carbon atoms,and wherein M is phosphorus, antimony, or arsenic.
 2. A catalyst systemaccording to claim 1 wherein the mole ratio of said elemental metal tosaid nitrosyl metal halide is in the range of about 0.75/1 to about 50/1and said elemental metal is a powder.
 3. A catalyst system according toclaim 2 wherein the nitrosyl metal halide is an iron nitrosyl halide. 4.A catalyst system according to claim 3 wherein said iron nitrosyl halideis selected from the group consisting of compounds having the formulas[Fe(NO)₂ Cl]_(y) or Fe(NO)₂ (L)Cl, wherein L is selected from the groupconsisting of tetrahydrofuran, triphenylphosphine, andtriphenylphosphine oxide.
 5. A catalyst system according to claim 1formed by contacting said at least one elemental metal with the reactionproduct mixture produced when an iron triad metal dihalide selected fromthe group consisting of iron dihalide and cobalt dihalide, wherein thehalide is selected from the group consisting of chloride, bromide, andiodide, is reacted with at least one alkali metal nitrite in a liquid inwhich said iron triad metal dihalide is at least partially soluble,under reaction conditions suitable for yielding a corresponding irontriad metal nitrosyl halide.
 6. A catalyst system according to claim 5wherein said iron triad metal dihalide is reacted with said at least onealkali metal nitrite in the presence of a compound (L) which forms aligand with said nitrosyl halide.
 7. A catalyst system according toclaim 6 wherein said iron triad metal dihalide is iron dichloride.
 8. Acatalyst system according to claim 1 formed by contacting said at leastone elemental metal with the reaction product mixture produced when aniron triad metal dihalide selected from the group consisting of irondihalide, cobalt dihalide, and nickel dihalide, wherein the halide isselected from the group consisting of chloride, bromide, and iodide, isreacted with at least one alkali metal nitrite in a liquid in which saidmetal dihalide is at least partially soluble and in the presence of atleast one elemental metal selected from the group consisting of thecorresponding iron triad metal and zinc, under reaction conditionssuitable for yielding a corresponding iron triad metal nitrosyl halide.